This continued study proposes to measure the quantitative increase in EFA requirement caused by dietary trans fatty acids. We also propose to feed a diet containing only c,c-18:2 (no c,t-18:2) to determine if any c,t-18:2 is produced in vivo from t-18:1, a fact we proved in vitro. We also propose to study the relative rates of enzyme systems which act upon isomeric fatty acids. This study will describe how double bond position and geometry affect the metabolism of fatty acids.